The present invention relates to a liquid crystal display device. More particularly, it relates to a liquid crystal display device which prevents sealing material from being uncured and presents high reliability even if a light shield film or wiring is provided in the proximity of an injection port for obtaining a high performance.
FIGS. 8 and 9 show diagrams of a device as disclosed, for instance, in Japanese Unexamined Patent Publication No. 44420/1983 as an example of a conventional liquid crystal device. Of these drawings, FIG. 8 is a plan view showing an arrangement of a conventional liquid crystal device, and FIG. 9 is a sectional view taken along the line IX--IX in FIG. 8.
In FIGS. 8 and 9, 21 denotes a pair of glass substrates on which there are formed transparent electrodes and metal wiring (not shown) on opposing face sides, 22 a seal material made of resin for adhering the pair of glass substrates 21 together, 23 an injection port formed at a part of the seal material 22 for injecting liquid crystal 25 therein, 24 spacer spread for maintaining a clearance between the pair of glass substances 21 constant, 25 liquid crystal injected into the clearance between the pair of glass substances 21, and 26 a sealing material provided for preventing leakage of the liquid crystal 25.
As for a material for the sealing material 26, UV curable resin might be employed as shown in Japanese Unexamined Patent Publication No. 44420/1983 in view of increasing throughput during the sealing process and the pot life (working life after mixing) of the material. As shown in FIG. 9, after application of the sealing material 26, a lamp generating ultraviolet light is employed for irradiating ultraviolet light in a direction as indicated by arrow 27 to perform curing of the sealing material 26 made of resin.
After application, the sealing material 26 is made to penetrate into the clearance between the pair of glass substrates 21 by means of capillary action with the aim of improving the sealing effects thereof so that it generally assumes a condition as shown in FIG. 9 in which the sealing material has penetrated between the two glass substrates 21. In FIG. 9, the part of the sealing material 26 that has penetrated between the pair of glass substrates 21 is cured by ultraviolet light 28 that comes around from a lateral direction (upper or lower direction in FIG. 9). In this manner, the part at which the sealing material 26 has penetrated presents high performance of sealing off an aperture of the injection port 23 whereby not only leakage of liquid crystal from the interior of the liquid crystal display device can be prevented but also high effects of preventing penetration of water or the like from the exterior can be obtained. Therefore, in order to improve the reliability of the device, the sealing material is positively made to penetrate between the glass substrate in manufacturing of liquid crystal display devices. Generally, such penetrating distance is adjusted to be approximately 0.1 to 1 mm.
Latest liquid crystal display devices of high performance are of arrangements as shown, for instance, in FIG. 10. 29 denotes a color filter substrate on which there is formed a color filter layer 31 for applying color to the display, and 30 a TFT substrate on which there is formed a thin film transistor. Further, since it is not desirable that light is transmitted through regions other than a display portion 32, a light shield film 33 employing chromium thin film or the like is formed in peripheral portions of one substrate 29 on regions other than the display portion. Especially in a TFT-LCD color liquid crystal display device as shown in FIG. 10 employing a substrate having formed thereon thin film transistor and a color filter substrate, such formation of light shield film is inevitable, and the light shield film is generally formed on the side of the color filter substrate.
On the other TFT substrate 30 having no light shield film formed thereon, there is formed a metal wiring 34 for signals driving the liquid crystal 25. Since the latest liquid crystal display devices of high performance are designed such that the size of the display portion with respect to the frame size is set to be maximum, the distance between the display portion and the circumferential line of the liquid crystal panel is small. Further, at a portion of the injection port of the liquid crystal display device, there is created a portion at which the sealing material 26 is sandwiched between the light shield film 33 and the metal wiring 34.
In this manner, in case the sealing material 26 has penetrated between the pair of glass substrates 29, 30 and at least a part of the sealing material 26 is sandwiched between films which do not transmit light such as the light shield film 33 or metal wiring 34, ultraviolet light or visible radiation can not be irradiated onto this sandwiched portion in an amount sufficient for curing so that some sealing material remains in an uncured condition. This uncured sealing material is in contact with liquid crystal, and during long-term use of the liquid crystal display device, the uncured sealing material gradually disperses into the liquid crystal, and the liquid crystal containing the dispersed sealing material therein causes degradations in voltage-transmittance characteristics or characteristics such as resistivity. Consequently, it caused degradations in display performance in the proximity of the injection port, or more particularly, local variations in luminance. Since especially a decrease in resistivity would cause fatal deficiencies in case of a TFT-LCD, it is necessary that sufficient curing of the sealing material is ensured.
For instance, FIG. 11 shows an example of luminance distribution of a liquid crystal panel in which the sealing material at the injection port has remained in an uncured condition. It can be understood from FIG. 11 that the luminance is partially higher in the proximity of the injection port of the liquid crystal panel. This is due to the fact that the resistivity of the liquid crystal has decreased at a portion in the proximity of the injection port.
The present invention has been made for solving such problems, and it is an object thereof to provide a liquid crystal display device of high reliability by making sealing material that has penetrated between a pair of glass substrates cure without remaining any uncured portions in order to prevent occurrence of display deficiencies owing to uncured sealing material.